One may wonder how large are the objects presented in the blog. Actually they are huge – hard to imagine their actual size, but many people are also interested in their apparent size in the sky. Well, the scale can be quite different. It is quite nice to compare this to some objects we can imagine to place at some distance and see. Let us start with big ones.
Near M31 galaxy there is another one – M33 in the Triangulum constelation. This one is a little bit further and also is a smaller galaxy. Apparent diameter of the M33 is about 1 degree, so about two times as apparent Moon diameter. However the outer arms of M33 are very faint and can be seen only in long exposured photos, like the one below:
But still, if we would be able to see M33 galaxy million times more luminous than it is the view would be magnificent! Using the same 1 cent coin you need to move it about 85cm away to make it look as large as M33 is in the sky.
There are a dozen or a little bit more galaxies with apparent size comparable with Moon diameter, and then we go deeper into the galaxies that are more distant. An example can be NGC4725 galaxy in the next picture. This one has apparent size of 1 cent coin placed about 5 meters away. So not an easy catch and not too many details could be seen there:
NGC4725 galaxy can be vieved using 6″ diameter telescope under dark sky, but do not expect to see more than just a little fuzzy blob in the sky. This galaxy is about 20 times more distant than described above M33 and M31.
There are of course much more galaxies – the deeper we look the more there are. Next picture shows Abell 347 galaxy cluster. It is about 200 million light years away, so the galaxies seem to be pretty small, but actually they are just quite distant. Using 12″ diameter telescope under dark sky you will be able to see a few of them as just little fuzzies in the dark background. The whole frame is about of the half of apparent Moon diameter, and the nice spiral galaxy at the upper right part has the apparent size of 1 cent coin viewed from 30 meters.
So still not so small, and can imagine this size, right? Well, lets do another step (in the apparent size, not actual distance) and take a look into high resolution picture of the Moon:
The tiny crater at the picture has diameter of 4km. But the magnification of this picture is quite large, and if you would like to use again our 1 cent coin to cover this crater we need to move the coin about 1.5km away. Such high resolution image can be done with bright objects (as planets or Moon) using different technique than for deep sky objects – in this case we use short exposures, then choose the best frames and stack them to get detailed picture. This way we can in some extent get rid of atmospheric turbulences effect that ruins resolution when observing from the Earth surface. Hubble Space Telescope has not this problem at all 🙂
At the end – kind of mosaic to present all this article pictures in one place. All pictures has been taken using moderate 6″ diameter newtonian telescope but using different cameras and techniques. When I started to be interested in astronomy (about 20 years ago) I would never imagine to obtain such results using so small telescope from the backyard. Things changed… 🙂